1. Field of the Invention
The present invention relates to an apparatus which quantifies faint fluorescent or phosphorescent luminescence which is biologically, chemically or electrochemically generated. In particular, the invention relates to a luminescence measuring apparatus which uses a photomultiplier tube for measurement.
2. Description of the Related Art
As a qualitative/quantitative analysis technique, it is known to use a substance which specifically binds to a constituent of the object to be assayed. The substance is labeled, and the constituent is identified and quantified by measuring the label. This technique is particularly effective when the amount of the constituent of interest is very small and therefore has been used in determining the presence or absence of antigens, antibodies, enzymes and particular genetic sequences in biological samples. In the past, a radioactive substance or the like was used as the label. However, since the radioactive substance cannot easily be handled due to the radioactivity and other problems, it has recently become common to use a luminescent substance as the label. The luminescent substance is such a bioluminescent substance as in a firefly or a chemiluminescent substance. Immediately before luminescence measurement is performed, a trigger substance is added to induce bioluminescence or chemiluminescence. For example, bioluminescence occurs when an enzyme-containing liquid is mixed with a liquid which contains the corresponding substrate since the substrate is oxidized by the enzyme and therefore excited to an active state resulting in luminescence. Whereas the amount of luminescence is proportional to the amount of the substrate, the amount of the substrate emitting luminescence is dependent on the concentration of the enzyme. Accordingly, it is possible to indirectly quantify the amount of the enzyme by measuring the amount of luminescence.
Conventional trace-fluorescence measuring apparatuses are such that a luminescent substance is put in a vessel shaped to have a larger height than the bottom and a detector is arranged to face the side or bottom of the tube-shaped vessel, allowing the measuring tool to measure the light emitted from the luminescent substance. Whether the detector is arranged to face the tube's side or bottom, a light reflector is set opposite to the measuring tool so that faint light can be detected. In this case, direct light escapes through a hole of the light reflector which is formed as part of the structure necessary to hold the tube. In addition, even if the structure to hold the tube is designed not to require the light reflector to have such a hole, light impinges on the structure resulting in a decrease in light intensity. Furthermore, light from the luminescent substance considerably decreases or decays in intensity before reaching the detector due to scattering and absorption during transmission through the liquid and the tube's wall.
In the case of the trace-luminescence measuring apparatus described in JP-A-2000-146825, when a test tube with a substance to be measured therein included is inserted, a shutter unit provided for the light reception unit is forced to move, allowing the light reception unit to directly receive light from the substance.